The present invention relates generally to exhaust fans, and more particularly to exhaust fans of the type that draw contaminated air from one or more fume hoods dispersed throughout a building, mix the contaminated air with ambient air to dilute the contaminants, and vent the diluted air from the building into the ambient environment.
There are many different types of exhaust systems for buildings. In most of these the objective is to simply draw air from inside the building in an efficient manner. In building such as laboratories, fumes are produced by chemical and biological processes, which may have an unpleasant odor, is noxious or toxic. One solution is to exhaust such fumes through a tall exhaust stack which releases the fumes far above ground and roof level. Such exhaust stacks, however, are expensive to build and are unsightly.
Another solution is to mix the fumes with fresh air to dilute the contaminated air, and exhaust the diluted air upwards from the top of the building at a high velocity. The exhaust is thus diluted and blown high above the building. Examples of such systems are described in U.S. Pat. Nos. 4,806,076; 5,439,349 and 6,112,850.
Among these systems, U.S. Pat. No. 4,806,076 discloses a system in which a fan motor has a motor shaft that is directly connected to a fan having rotating fan blades that draw contaminated exhaust air from the building and blow the exhaust air up into the ambient environment. Unfortunately, the bearings that support the motor shaft inside the motor absorb the thrust loads imparted by the fan during operation, thus increasing wear on the motor. Furthermore, because the interface between the motor shaft and the fan is located in an area that receives exhaust air during operation, a person is required to enter an area that is polluted with contaminants when motor maintenance operations involve detachment of the motor shaft from the fan.
What is therefore desired is a building exhaust system including a building exhaust stack coupled to a fan that overcomes the deficiencies associated with conventional systems.